1. Field of the Invention
The invention relates to image intensifiers, particularly with respect to microchannel plate image intensifiers. The invention relates to the control of sensitivity and protection from damage in systems utilizing such image intensifiers.
2. Description of the Prior Art
Systems are known in the prior art utilizing image intensifiers such as the present day design of microchannel plate image intensifiers. Such systems include intensified focal plane array television camera systems as well as directly viewed intensifier systems as, for example, for periscopes. Such systems employing image intensifiers are generally limited in dynamic range so that blooming occurs when the input light level becomes high or damage occurs when the input light level becomes excessively high. The prior art systems primarily utilized automatic brightness control (ABC) to alleviate the problems by controlling the gain of the microchannel plate. The prior art automatic brightness control does not protect the photocathode of the image intensifier since such arrangement only controls gain after the photocathode which is the sensitive component of the device. This prior art control, therefore, permits damage to the photocathode of which the observer is unaware. Such automatic brightness control systems additionally have limited dynamic range and no capability of repairing accidental damage.